This invention is related to the field of processes that polymerize ethylene, or that polymerize ethylene and at least one other olefin, to produce a polymer.
There are many processes that polymerize ethylene, or that polymerize ethylene and at least one other olefin, to produce a polymer. There are also many manufacturing processes that use these types of polymers to produce useful items. One of these manufacturing processes is called blow molding.
In general, blow molding is useful for producing hollow plastic products. A principle advantage of blow molding is its ability to produce hollow shapes without having to join two or more separately molded parts.
In order to produce a good quality blow molded product, one needs to start with a good quality polymer. However, producing such good quality polymers is difficult. It has been especially difficult to produce a good quality polymer that has a high environmental stress crack resistance (ESCR) and that is useful for blow molding applications.
Therefore, the inventors provide this invention so that such good quality polymers with high ESCR""s are more readily obtainable, and readily useable in blow molding applications.
It is an object of this invention to provide a process to polymerize ethylene, or ethylene and at least one other olefin to produce a polymer.
It is also an object of this invention to provide said polymer.
In accordance with this invention a process is provided. The process comprises (or optionally xe2x80x9cconsists essentially ofxe2x80x9d, or xe2x80x9cconsists ofxe2x80x9d) polymerizing ethylene, or polymerizing ethylene and at least one other olefin, to produce a polymer,
wherein said polymerizing is conducted in a polymerization zone, and
wherein said polymerizing is conducted using a catalyst and a cocatalyst, and
wherein said catalyst comprises chromium on a support, and
wherein the amount of said chromium on said support is from about 0.5 to 5 weight percent, and
wherein said support comprises silica, in major part, and
wherein the amount of titanium in said support is greater than about 3.5 to about 10 weight percent based on the weight of said support, and
wherein said support has a surface area from about 400 to about 800 square meters per gram, and
wherein said support has a pore volume from about 1.8 to about 4 cubic centimeters per gram, and
wherein said catalyst has been activated at a temperature in the range of about 600xc2x0 F. to about 1100xc2x0 F. in the presence of an oxidizing ambient, and
wherein said cocatalyst is an organoboron compound.
In accordance with this invention a polymer comprising the following properties: a density from about 0.94 to about 0.96, a high load melt index from about 5 to about 45 g/10 min., a shear ratio (high load melt index/melt index) from about 150 to about 400, a heterogeneity index from about 15 to about 55, an ESCR condition A greater than about 1000 hours, and ESCR Condition B greater than about 200 hours, a normalized die swell from about 0.8 to about 1.1, a weight swell from about 300 to about 500 percent, and an onset of melt fracture greater than about 2000 secxe2x88x921.
These and other objects will become more apparent with the following.
The terms xe2x80x9ccomprisexe2x80x9d, xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d are open-ended and do not exclude the presence of other steps, elements, or materials that are not specifically mentioned in this specification.
The phrases xe2x80x9cconsists ofxe2x80x9d and xe2x80x9cconsisting ofxe2x80x9d are closed ended and do exclude the presence of other steps, elements, or materials that are not specifically mentioned in this specification, however, they do not exclude impurities normally associated with the elements and materials used.
The phrases xe2x80x9cconsists essentially ofxe2x80x9d and xe2x80x9cconsisting essentially ofxe2x80x9d do not exclude the presence of other steps, elements, or materials that are not specifically mentioned in this specification, as along as such steps, elements, or materials, do not affect the basic and novel characteristics of the invention, additionally, they do not exclude impurities normally associated with the elements and materials used.
The previous terms and phrases are intended for use in areas outside of U.S. jurisdiction. Within the U.S. jurisdiction the above terms and phrases are to be applied as they are construed by U.S. courts and the U.S. Patent Officeu.
This polymerization can be carried out in any manner known in the art such as gas phase, solution or slurry polymerization conditions. A stirred reactor can be utilized for a batch process, or the reaction can be carried out continuously in a loop reactor.
This polymerization is conducted in a polymerization zone. It is preferred to conduct this polymerization in a loop reactor. It is more preferred when said polymerization is conducted in a loop reactor under slurry polymerization conditions. Currently, the preferred diluent for slurry polymerization is isobutane.
Loop reactors are known in the art, see, for example, U.S. Pat. Nos. 3,248,179; 4,424,341; 4,501,855; and 4,613,484; the entire disclosures of which are hereby incorporated by reference. Especially preferred processes are disclosed in U.S. Pat. Nos. 4,589,957; 4,737,280; 5,597,892; and 5,575,979 the entire disclosures of which are also hereby incorporated by reference.
A preferred polymerization technique is that which is referred to as a particle form, or slurry process, wherein the temperature is kept below the temperature at which polymer swells and fouls the reactor. Such polymerization techniques are well known in the art and are disclosed, for example, in Norwood, U.S. Pat. No. 3,248,179, the disclosure of which is hereby incorporated by reference.
Two preferred polymerization methods for the slurry process are those employing a loop reactor of the type disclosed in Norwood and those utilizing a plurality of stirred reactors either in series, parallel or combinations thereof wherein the reaction conditions are different in the different reactors.
The diluent, before it enters the reactor, comprises isobutane. Additionally, before the diluent enters the reactor, the majority of said diluent is isobutane. It is preferred when the diluent contains 60-100, more preferably, 70-100, and most preferably 80-100 weight percent isobutane based on the weight of the diluent before it enters the reactor.
The polymerization is conducted at a temperature from about 190xc2x0 F. to about 230xc2x0 F. However, it is preferred when said polymerizing is conducted at a temperature from about 195xc2x0 F. to about 225xc2x0 F. and it even more preferred when said polymerizing is conducted at a temperature from 200xc2x0 F. to 220xc2x0 F. At temperatures below about 190xc2x0 F. the efficiency of the catalyst and the reactor is adversely affected. At temperatures above about 230xc2x0 F. the reactor could foul due to the swelling of the polymer.
The pressure that the polymerization is conducted at is in the range of about 400 psia to about 800 psia, preferably about 500 psia to about 700 psia. The catalyst used in this invention comprises chromium on a support, preferably in the form of chromium oxide on a support. The amount of chromium on said support is in the range of about 0.5 to about 5 weight percent, preferably about 1 to about 4 weight percent, and most preferably from 1.5 to 3 weight percent, where such weight percents are based on the weight of the support.
The support comprises silica and titania. Additionally, such support has silica, as its major component by weight, and titania, as its minor component by weight. It is most preferred when said support consists essentially of silica and titania, with little, if any, impurities. It is even more preferred when the silica and titania are cogelled.
It is preferred when the amount of titanium in the support is from about 3.5 to about 10 weight percent, preferably about 4 to about 8 percent, and most preferably from 4 to 6 weight percent, where said weight percents are based on the weight of the support. When the amount of titanium is less than about 3.5 weight percent, the ESCR of the resin produced tends to be too low. When the amount of titanium is greater than about 10 weight percent, the catalyst becomes thermally unstable and processability of the resin produced tends to be undesirable.
The support should have a surface area from about 400 to about 800 square meters per gram. It is more preferred when the support has a surface area from about 425 to 700 square meters per gram, and it is most preferred when said support has a surface area from 450 to 650 square meters per gram. Surface areas below about 400 m2/g tend to have less activity, less ESCR, and too little die swell, while surface areas above about 800 m2/g produces polymers that have a die swell that is too high, an amount of long chain branching that is too low, and possibly, a melt index that is too low.
The support should have a pore volume from about 1.8 to about 4 cubic centimeters per gram. It is more preferred when the support has a pore volume from about 1.9 to about 3 cm3/g, and it is most when said support has a pore volume from 2 to 2.7 cm3/gram. Pore volumes below about 1.8 cm3/g produce polymer with low ESCR, while pore volumes above about 4 cm3/g are difficult to handle in commercial operations.
Methods of producing these types of catalysts are known in the art. See for example, U.S. Pat. Nos. 3,900,457; 4,081,407; 4,392,990; 4,405,501; 4,735,931; 4,981,831; the disclosures of which are hereby incorporated by reference.
The catalyst should be activated in the presence of an oxidizing ambient (sometime referred to as xe2x80x9catmospherexe2x80x9d) at a temperature greater than about 600xc2x0 F. to about 1100xc2x0 F. It is even more preferred when the temperature is from about 700xc2x0 F. to less than 1100xc2x0 F., and it is even more preferred when the temperature is from about 900xc2x0 F. to about 1090xc2x0 F., and it is most preferred when the temperature is from about 900xc2x0 F. to about 1050xc2x0 F. At temperatures below about 600xc2x0 F. the activity of the catalyst is reduced and the physical properties of the polymer are adversely affected. At temperatures above about 1100xc2x0 F. there is a loss of ESCR in the polymer. Currently, the preferred oxidizing ambient is air. This activation is carried out for a time period of about 1 minute to about 50 hours. This allows a portion of the chromium in a lower valance state to be converted to a hexavalent state.
The ethylene used should be polymerization grade ethylene. The other olefins that can be used are alpha-olefins having from 4 to 12 carbon atoms. Currently, 1-butene, 1-hexene, and 1-octene are the most preferred olefins.
The catalyst must be used in the presence of a cocatalyst that is an organoboron compound. Organoboron compounds, as used in this invention, have the following general formula: B(X)3.
In this formula (X) is a hydrocarbyl having from 1-20 carbon atoms. Currently, it is preferred when (X) is an alkyl having from 1 to 10 carbon atoms. However, it is most preferred when (X) is selected from the group consisting of methyl, ethyl, propyl, butyl, and isobutyl.
Examples of such compounds are as follows:
trimethylboron;
triethylboron;
tripropylboron;
tributylboron; and
triisobutylboron.
Currently, triethylboron is preferred.
The amount of organoboron compound to use in this invention is from about 1 to about 15 parts per million by weight, based on the weight of the diluent before it enters the reactor. However, it is preferred when the amount is from about 1 to about 10, and it is most preferred when the amount is from 2 to 4 parts per million.
The polymer produced needs to have the following properties in order to be a polymer that is good for blow molding applications.
The density needs to be from about 0.94 to 0.96 grams per cubic centimeter. However, it is preferred when the density is from about 0.95 g/cm3 to 0.96 g/cm3 and it is more preferred when the density is from 0.953 g/cm3 to 0.958 g/cm. This density is determined in accordance with ASTM D1505.
The high load melt index needs to be from about 5 to about 45 grams per ten minutes. However, it is preferred when the high load melt index is from about 8 g/10 min to about 35 g/10 min. and it is even more preferred when the high load melt index is from 10 g/10 min. to 25 g/10 min. This high load melt index is determined in accordance with ASTM D 1238.
The shear ratio (HLMI/MI) needs to be from about 150 to about 400. However, it is preferred when the shear ratio is from about 170 to about 350 and it is even more preferred when the shear ratio is from 180-320.
The heterogeneity index (Mw/Mn) needs to be from about 15 to about 55. However, it is preferred when the heterogeneity index is from 20 to 50 and it is even more preferred when the heterogeneity index is from 25 to 45, and it is most preferred when the Heterogeneity index is from 30 to 40. The heterogeneity index was determined by gel permeation chromatography.
The ESCR Condition A of the polymer is greater than 1000 hours. The ESCR Condition B of the polymer is greater than 200 hours, preferably greater than 300 hours. These ESCR""s are measured according to ASTM D1693, Conditions A and B. Additionally, the polymer should have a bottle ESCR greater than 700 hours as measure in accordance with the examples below.
The die swell is an indication of how much the molten polymer tends to flare out as it is extruded from the die. The normalized die swell should be between about 0.8 and about 1.1, preferably, about 0.9 and about 1.05, and most preferably, from 0.95 to 1.05. Normalized die swell outside this range leads to poor bottle molding. High die swell results in the parison extending beyond the mold, leading to, for example, xe2x80x9cpinch-offxe2x80x9d or other problems. Low die swell can cause a failure to fill the mold.
Weight swell is a measure of how much memory the polymer retains as it is extruded. A 300 weight percent swell indicates that the final bottle wall thickness is three times the die gap distance. If the polymer has a characteristically high weight swell, it requires a smaller die gap to produce the required wall thickness, and a smaller gap can restrict polymer flow, and thus machine output. The weight swell should be between about 300 and about 500 weight percent, preferably, about 325 and about 475 weight percent, and most preferably, from 350 to 450 weight percent.
The onset of melt fracture should be greater that 2000 secxe2x88x921.